Controllable condition rotary drive system

ABSTRACT

A system comprising a pair of reversible hydraulic motors driving a common rotary output shaft such as a machine tool drive lead screw or the like. A control system consisting of a hydraulic transfer valve for selectively coupling the hydraulic motors in either a series or parallel drive arrangement to selectively obtain high-torque low-speed or low-torque, highspeed mode of operation during either forward or reverse drive conditions. An actuator for the transfer valve and a flowreversing valve both adapted to be separately responsive to electrical digital-type signals of the type generated by numerical machine tool computer control systems.

United States Patent Lewis [4 1 Jan. 18, 1972 [54] CONTROLLABLE CONDITION ROTARY DRIVE SYSTEM [72] Inventor: Richard J. Lewis, New Hartford, N .Y.

[73] Assignee: The Bendix Corporation [22] Filed: Sept. 18, 1970 [21] Appl. No.: 73,474

3,348,624 10/1967 Just et a]. ..60/53 R X Primary Examiner-Edgar W. Geoghegan Attomey-Bruce A. Yungman [57] ABSTRACT A system comprising a pair of reversible hydraulic motors driving a common rotary output shaft such as a machine tool drive lead screw or the like. A control system consisting of a hydraulic transfer valve for selectively coupling the hydraulic motors in either a series or parallel drive arrangement to selectively obtain high-torque low-speed or low-torque, high-speed mode of operation during either forward or reverse drive conditions. An actuator for the transfer valve and a flow-reversing valve both adapted to be separately responsive to electrical digital-type signals of the type generated by numerical machine tool computer control systems.

9 Claims, 4 Drawing Figures Pmmmmwm 3.635022 SHEET 1 BF 4 RICHARD J. LEW/8 INVENTOR.

PATENTEDJAMBIBR 3 35x SHEET 2 BF 4 RICHARD J. LEW/S INVENTOR.

CONTROLLABLE CONDITION ROTARY DRIVE SYSTEM FIELD OF THE INVENTION The present invention relates to a hydraulic rotary drive system, and more particularly to a drive system for the drivescrew of a machine bed which is adapted for numerical machine control.

DESCRIPTION OF THE PRIOR ART There are many industrial applications in which a simple multiple-speed variable-torque motor is necessary or desirable. In multiple-motor systems of the type in which a plurality of motors are supplied with fluid from a single pump, there are two basically difierent ways in which the motors may be connected with the pump. In one arrangement, hereinafter called the series arrangement, the pump supplies fluid to a first motor from which the fluid passes to a second motor and so on throughout the series. The fluid flows from the last motor in the series to the sump from which the pump draws fluid. In the other arrangement, hereinafter called the parallel arrangement, the pump draws fluid from a sump and supplies it to a manifold to which the inlet connections of all the motors of a system are connected. The motor exhaust connections all communicate with a manifold which is connected to the sump. The system preferably, but not necessarily, includes a directional control or reversing valve which in the series arrangement will reverse the order and direction of flow through the plurality of motors, and which in the parallel arrangement will serve to reverse the connections between the manifold and the pump and sump respectively. These prior art systems, however, did not provide for series and parallel operation for both forward and reverse drive conditions.

There are other solutions which have been used to provide low-speed control and high-speed traverse on machine tools, but these mainly require a larger oil supply in order to accomplish high motor speed, and two servo loops in the machine controller, one for the high-gain portion and one for the lowgain portion of cycle. One such device has been a dual gain servo valve, wherein the gain of the servo valve is low at lowinput conditions and then this gain slope makes an abrupt change such that the gain is higher at the higher input conditions which would be used for the traverse of the machine tool. It should be noted that low gain slope is required for proper control in the low-speed or cutting mode. in addition to the disadvantages listed above, the dual gain servo valve cannot switch modes at a random motor speed.

Each arrangement has some characteristics which are advantageous and some which are not. A series arrangement is characteristically a highspeed system, but the available torque is limited. The parallel arrangement is characteristically a low-speed, high-torque system. Frequently a single multiple-motor system must have the attributes of both systems. The present day drive systems are limited in that they can only supply accurate control over low speed with a sacrifice in high-speed operation or have high-speed operation with a sacrifice in low-speed control. This limitation is due to the servo valve flow to input gain. A very low flow gain is required to control a motor at low speeds, whereas a high gain is required for high-speed operation. A controllable condition rotary drive system is a unitary system which supplies power in either of two modes for both forward and reverse drive conditions. The necessity of this type of drive system stems from the recent trend of the machine manufacturers to couple the hydraulic drive system directly to the drivescrew of a machine bed. This application requires a very accurate control of speed, from a fraction of a revolution per minute up to thousands of revolutions per minute.

SUMMARY OF THE INVENTION The present invention offers both low-flow gain at low speeds and high-flow gain at high speeds with the same servo valve (hereafter referred to as a flow control or reversing valve.) To accomplish this the valve is sized to offer good lowspeed, low-flow gain operation. The output drive shaft is driven by two equally sized reversible hydraulic motors. By supplying flow to both motors at their inlet and discharging from both motors, the two motors offer parallel operation. When high-flow gain is required, the flow through the motor is changed to flow into the inlet of the first motor, discharging to the inlet of the second motor and discharging from the second motor to the valve. This connection offers a series operation providing double the speed per gallon flow as in the parallel connection. Thus, with one reversing valve we now have two distinct outputs offering both low-flow gain and high-flow gain in the same drive mechanism. Both of these modes are controlled by one servo loop as the valve gain and motor dynamics remain the same for both modes. This then allows the machine tool programmer to select the low-speed, high-torque mode for cutting action where precise control of the machine is necessary and to select the high-speed mode for a rapid traverse of the machine without requiring a larger hydraulic power supply. Mode switching can be accomplished by use of the M function or profile machine controllers such as the Bendix Dynapath, or by sensing the reversing valve s control signal with a circuit that has been developed for this purpose. The dual mode reversible drive motor concept is a novel approach to the prior art problem, since the two motors may easily operate in a high gain for traverse of in low gain for control. This invention has at least three major advantages: (1 the hydraulic power supply needs to be only half the size for a given maximum traverse speed, (2 only one control loop is required on the machine controller for the axis, and (3 the mode change may be accomplished at any motor speed for both forward and reverse drive conditions. The control mode represents a high cubic inch displacement per motor revolution, and the traverse mode represents a low cubic inch displacement per motor revolution.

The present invention consists of five major components, a hydraulic transfer valve, a flow-reversing valve, a hydraulic actuator, and two hydraulic motors adapted to drive the same shaft. High-pressure flow from a pump is directed to the flow control valve, the actuator and a spool-positioning member within the hydraulic transfer valve.

The commercial embodiment of this invention employs a Bendix 58Vl5 Electro-hydraulic Flow Control Valve with a 3,000 p.s.i. rating which serves as the flow-reversing valve. A three-way 3,000 p.s.i. solenoid valve manufactured by Skinner Electric Valve Division, part number A14 DX7, serves as the actuator for the hydraulic transfer valve.

While operating in the parallel mode, flow from the reversing valve is routed to the hydraulic transfer valve and then to the motors inlet ports. The flow discharging from the motors returns to the reversing valve. A spool within the hydraulic transfer valve is held in the parallel position by the actuating or solenoid valve which pressurizes a chamber within the hydraulic transfer valve thereby overcoming the constant force of the pressurized fluid within a chamber inside the spool. When a mode change is required, the actuating valve is energized, thus allowing the pressurized chamber within the transfer valve to vent to the sump. With this drop in pressure, the spool which is under inlet pressure is force to its series position. In this position, flow from the reversing valve goes to the transfer valve and then directly to one of the motors. Discharge from this motor goes back to the switching valve where the fluid is rerouted to enter the inlet of the second motor. Discharge from this motor returns to the transfer valve and then back to the reversing valve which returns the flow to the sump.- Unlike prior art, switching modes are triggered by an external electrical signal to the actuator and not by internal load differential pressure.

The two motors may operate out of phase with respect to one another in order to provide smooth shaft rotation. Also, the spool within the transfer valve is designed to prevent any blocking of flow from the motors when switching modes.

A breadboard unit comprising the preferred embodiment of this invention has been developed and tested. A pair of standard 3,000 p.s.i. four-vane, six-lobe cam motor elements, both with the same displacement, as shown by FIG. 3 and to be described herein, were used. The tests were conducted with 0.6 cubic inch per revolution cam motors, so that the dual motor operated as a 0.6 CI/R motor in the series mode and 1.2 CI/R motor in the parallel mode. In the series mode the two elements shared the total pressure drop such that each motor element ran with approximately one-half the total pressure drop, but each element used the full output flow from the reversing valve. In the parallel mode both elements experienced the full pressure drop but they shared the flow, with each element taking approximately one-half the total flow.

In order to provide a motor suitable for use in applications where the inertial loads are high, it is sometimes necessary to provide cross port relief valves to prevent overpressure in the motor elements when the inertial loads tend to drive the motor when the servo valve is moved to null. A cross port bleed system can also be provided to attenuate the valve output and provide a stable system. The commercial embodiment of this invention includes both of these features; these features are old in the art, however. and are not a required part of this invention.

A test program was conducted on the system using various hydraulic stands to check the design features of the unit. FIG. 4, referred to infra, indicates the motor torque versus speed characteristics that were obtained when running this unit at a constant speed using a test stand that had a power-absorbing pump as a load device. FIG. 5, referred to infra, indicates the flow versus speed characteristics taken at the same time and illustrates the difference in flow when the mode is switched from a series mode of operation to a parallel mode of operation. In normal practice the series mode would be used only for high-speed operation and the parallel mode for low-speed operation.

This system was installed on an inertia-type test stand and the mode was switched intermittently as a flywheel accelerated from rest up to 1,800 r.p.m. FIG. 6 illustrates a trace from an X-Y" plotter of the torque versus speed characteristic during this form of test. It indicates smooth and steady switching at all speeds.

An open loop test was run on this system under no-load conditions. The data obtained through a comparison of the input signal to the reversing valve with the signal output from a tachometer mounted on the drive shaft indicated that there was no dynamic difference between the operation in series mode and operation in parallel mode. Since there is no difference in the dynamic data, both of the modes will operate from the same closed loop circuit on the machine controller, and this feature was successfully demonstrated by tests on a typical machine tool.

The breadboard unit of this system was tested on a Pratt & Whitney Keller Machine; the unit was installed on the X-axis of the machine and it was demonstrated that only one servo loop was required for proper control. Mode switching was accomplished by use of an M function. A program was prepared for the machine which switched both the mode and feed rate in the same command block. This mode change was rapid and smooth, indicating excellent control. Data from this test showed that the feed rate change need not be made until the unit is very close to the cut location. There was some indication that the changeover can occur as close as 0.001 inch to the location of cutting.

It is an object of this invention to provide a rotary drive system which offers good low-speed control with a corresponding advantage of high-speed operation for traverse for both forward and reverse drive conditions.

It is a further object of this invention to provide a controllable condition rotary drive system which can switch operating modes at the command of the programmer regardless of the existing motor speed.

It is still a further object of this invention to provide a dual mode reversible rotary drive system that requires only one servo control loop on the machine controller for the axis.

It is another object of this invention to provide a dual mode reversible drive system wherein the mode selection is accomplished by supplying a hydraulic signal to a transfer valve, said signal being generated by an actuating valve that operates in response to a machine controller of a single closed servo loop.

It is yet another object of this invention to provide a dual mode reversible rotary drive system in which the hydraulic power supply needs to be only one-half the size for a given maximum traverse speed. Thus, a machine tool builder can select a hydraulic power supply suitable for the machining mode and use the same supply for the higher speed traverse mode. Not only does this allow for a smaller power supply but the hoses, fittings, coolers, filters and blocking valves may also be greatly reduced in size and thus in cost.

This invenu'on further resides in certain novel features of construction and combinations and arrangement of parts, and further objects and advantages thereof will be apparent to those skilled in the art to which it pertains from the following description of the present preferred embodiment thereof.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram partly in axial section showing the essential elements of the invention when in the parallel mode of operation.

FIG. 2 is a schematic diagram partly in axial section showing the essential elements of the invention when in the series mode of operation.

FIG. 3 is an end plan view of a cam motor to be used in accordance with this invention.

FIG. 4 is a test run graph of motor torque in inch-pounds versus motor speed in revolutions per minute of this invention.

FIG. 5 is a test run graph of flow in gallons per minute versus motor speed in revolutions per minute, said data corresponding to the same test run illustrated in FIG. 4.

FIG. 6 is a plot of motor torque in inch-pounds versus motor speed of this invention when run on an inertia-type test stand.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Refer first to to FIG. 1. Reference numerals 11 and 12 indicate respectively a pump and a sump from which the pump draws fluid. Fluid enters the hydraulic transfer valves housing designated generally as 10, through port 13 and is then transferred through channel 14 to the inlet port 15 of the reversing valve designated generally as 16. Channel 14 extends further through the transfer valves housing 10 to an inlet 17 in the actuating valve 18. Fluid leaves the reversing valve 16 through a port 19 and passes through channel 20 to a valve bore 21 through port 22. Valve bore 21 extends axially the entire length of the housing 10. Fluid exits the valve bore 21 through corresponding port 122 continuing through channel 20 to an entrance port 23 in a first motor designated generally by the letter M,,. Simultaneously therewith the fluid exits an additional port 24 in housing 10 and is directed through channel 25 to an entrance port 26 in a second motor designated generally as M,,.

Fluid exits motor M to the valve bore 21. The fluid is then directed by means of a spool 51 to a port 32. Simultaneously fluid exits motor M through a port 31 and is transferred through a channel 30 to port 132. The discharged fluids from the two motors M and M, join at port 32 and are then communicated to the reversing valve 16 through channel 30. The fluid is then returned to the sump 12 through a port 35 by means of a channel 34.

Valve bore 21 is encircled by four peripheral grooves 40, 41, 42 and 43. Ports 32 and 132, 29, 24, 22 and 122 provide access to grooves 40, 41, 42 and 43 respectively. Grooves 40, 41, 42 and 43 communicate with channels 30, 28, 25 and 20 respectively. Valve spool 51 is slidably interposed within the valve bore 21. Three lands 60, 61 and 62 are formed on spool 51 and are axially separated from one another by encircling spool grooves 65 and 66. Land 62 of the spool 51 and valve bore 21 fonn a chamber 70 at the right end of spool 51. Land 611 and the valve bore 21 form a chamber 60 at the left side of spool 51. Spool 51 has a bore 95 therein at its left side permitting it to be slidably mounted to a spool-positioning member 90 which member extends axially within valve bore 21. Member 91) is mounted to housing and has a channel 91 therein which communicates with channel 14 and with bore 95 within spool 51.

Fluid from channel 14 enters actuating valve 18 through port 17 in housing 16. The fluid passes through channel 100 from valve 16 into chamber 70, thus biasing spool 51 toward the left as illustrated in FIG. 1.

In the preferred embodiment illustrated, M and M, are equally sized reversible hydraulic motors mounted to the same shaft designated generally by the numeral 110. A plan end view of these motors is shown in FIG. 3. Note that for purpose of illustration P, represents the supply pressure for the parallel mode of operation shown in FIG. 1 whereby the motors cause shaft 110 to rotate in a clockwise direction. When operating in the series mode, explained below, I represents the supply pressure to the motors which causes a counterclockwise rotation of shaft 110. It must be remembered, however, that the flow paths indicated in channels 20, 25, 28 and may be reversed by reversing valve 16 for either the parallel or series mode of operation. Thus, P in FIG. 1 may also represent the supply pressure for a parallel mode of operation that would cause a counterclockwise rotation of shaft 110 tantamount in rotational direction to the series mode shown in FIG. 2.

Referring to FIG. 2, the rotary drive system is illustrated in its series mode of operation. In this position land 62 is in contactive engagement with stop 130 at the right end of the valve bore 21. In this mode actuating valve 18 directs fluid through channel 34 and then in turn through channel 120 into chamber 80 within the valve bore 21. Simultaneously reversing valve 16 directs fluid through port 33 and then in turn through channel 30, through groove in the valve bore 21 to motor M, through port 31. Fluid exits motor M through port 26 and then travels through channel 25 to groove 42 within the valve bore 21. Because of its changed position within the valve bore 21, the fluid is directed by spool 51 to groove 41, then from groove 41 through channel 28 to motor M, through port 27. The fluid returns to the reversing valve 16 by exiting motor M, through port 23 and then passing through channel 20 to port 19 in reversing valve 16; here the fluid passes directly through valve bore 21 by means of peripheral groove 43.

In both modes of operation pump 11 constantly supplies fluid under pressure to bore 95 within spool 51 by means of channel 14 and channel 91 within member 90.

OPERA'I'IONPARALLEL MODE Referring to FIG. 1, as above described, the present invention consists of tive major components: the reversing valve 16, the actuating valve 16, a transfer valve containing spool 51 therein, and two reversible hydraulic motors designated as M, and M,,. High-pressure flow from pump 11 is directed simultaneously to the reversing valve 16, actuating valve 18 and the spool-positioning member 911. While operating in the parallel mode, flow from the reversing valve 16 is directed through channel 211 to the spool valve bore 21. Upon entering the valve bore 21 the fluid is permitted to exit through ports 122 and 24 due to the peripheral grooves 43 and 42 respectively within the housing 10. The fluid then passes through channels 20 and 25 to the inlet ports 23 and 26 respectively of motors M, and M,,. The flow discharging from motors M and M, returns to the valve bore 21 through channels 311 and 28 respectively. Peripheral grooves 41) and 41 in housing 10 communicate the discharged fluid to a common discharge port 32. The fluid is then returned to reversing valve 16 through channel 30. The spool 51 is held in the parallel position by energizing actuating valve 16. When valve 18 is energized, denoted by electrical signal Se it allows the pressurized fluid to enter chamber 70 within valve bore 21 by means of channel 100, thereby overcoming the force of the pressurized fluid in chamber within spool 51 at the opposite end of the valve bore. Both the actuating valve 18 and the reversing valve 16 are energized by external electrical signals generated whenever a mode change and/or change in rotational direction of shaft 110 is necessary or desired. Se, and Se are the signals for the actuating valve and the reversing valve respectively when operating in the parallel mode for clockwise rotation of shaft 110, and Se and Se, represent the signals for the parallel mode for counterclockwise rotation of shaft 110. Thus, it is the external electric signal and not internal load differential pressure that triggers the switching of modes. By supplying flow to both motors at their inlet and discharging from both motors to discharge, the two motors ofier parallel operation. Both motors take approximately one-half the total flow, and both experience the full pressure drop. In this mode of operation the system offers high-torque and low-speed operation.

OPERATIONSERIES MODE When a mode change is required, that is, high-speed, lowtorque operation is desired, the actuating valve 18 is again energized, denoted by signal se thus, allowing the pressurized chamber 70 to vent through channel back to valve 18 and then through channel 34 back to sump 12. By eliminating the pressure on land 62 of spool 51, the hydraulic signal communicated through spool-positioning member 90 which pressurizes chamber 95 within spool 51 forces the spool into contactive engagement with the stop 130. By simultaneously providing another signal Se, to reversing valve 16, valve 16 directs fluid through channel 30 to inlet port 31 of motor M passing directly through peripheral groove 40. Discharge from motor M now passes through channel 25 to groove 42 within housing 10. The fluid then exits the valve bore 21 through groove 41 within housing 10 to the inlet port of motor M, by means of channel 28. The discharge from motor M, is then communicated directly back to reversing valve 16 through channel 20 passing directly through peripheral groove 43 within housing 10. The fluid returns to sump 12 from reversing valve 16 by means of channel 34. Thus, both the mode of operation and the direction of rotation of shaft are changed. However, if reversing valve 16 was not energized simultaneously with actuating valve 18, shaft 110 would continue to rotate in a clockwise direction but at twice the speed per gallon flow. That is each motor utilizes the full output flow from the reversing valve, and each motor operates with approximately one-half the total pressure drop. The speed of switching from the parallel to the series mode of operation is increased by supplying an additional hydraulic force to land 60 of spool 51. This is accomplished by the direction of a hydraulic signal from actuating valve 18 through channel 34 and then through channel into chamber 80. Thus, with one reversing (servo) valve we now have two distinct outputs offering both low-flow gain and high-flow gain in the same drive mechanism for either the forward or reverse (that is, clockwise or counterclockwise) drive condition.

In order to provide smooth shaft rotation, the two motors Ml and M operate out of phase with respect to each other.

In addition to the novel features of the present invention mentioned above, the valve spool and groove design of the valve bore ofler an even additional novel feature. Making the axial length of peripheral groove 42 larger than the axial length of center land 61 of the spool 51 prevents any possible blocking of flow from the motors when switching modes.

While a preferred embodiment of the invention has been disclosed, it will be apparent to those skilled in the art that changes may be made to the invention as set forth in the appended claims, and, in some cases, certain features of the invention may be used to advantage without corresponding use of other features. Accordingly, it is intended that the illustrative and descriptive materials herein be used to illustrate the principles of the invention and not to limit the scope thereof.

Iclaim:

first and second reversible hydraulic motors adapted to be drivably connected to a common output shaft:

a low-pressure fluid source;

a low-pressure fluid sump;

passage means interconnecting said fluid source and sump to said first and second hydraulic motors; motors;

an electrically controllable reversing valve operative with said passage means to reverse the fluid source and fluid sump connections selectively in response to a first electrical signal and thereby reverse the direction of rotation of said hydraulic motors;

a hydraulic transfer valve operative with said passage means to switch interconnection between said hydraulic motors from parallel to series fluid connection; and

an actuating valve responsive to a second electrical signal to actuate said transfer valve to selectively switch between series and parallel fluid connection during either forward or reverse motor drive conditions;

so that said common output shaft may rotate in either of two directions when said motors are either in a parallel or in a series fluid connection.

2. A dual mode reversible drive system comprising in combination a low-pressure fluid sump:

a high-pressure fluid source;

a flow control valve, said valve supplied fluid from said fluid source;

a solenoid-controlled valve, said valve supplied fluid from said fluid source;

switching means which receives fluid from said flow control valve, said switching means being activated by hydraulic signals from said solenoid-controlled valve;

a pair of motors, said motors having reversible inlet and discharge ports, said motors being in communication with said switching means through said ports such that said motors operate either in a parallel or in a series relationship; and

said motors drivingly connected to a single shaft.

3. The combination as recited in claim 2 wherein said switching means comprises:

a housing, said housing having a longitudinal cylindrical bore therein, said bore having a plurality of peripheral grooves separated by flangelike lands;

said housing having a plurality of vertical passages intersecting said grooves forming a plurality of ports therein, a plurality of said passages being in communication with the flow control valve, and a plurality of said passages being in communication with the motors inlet and discharging P a spool-positioning member;

a spool valve disposed in said cylindrical bore, said valve being axially aligned and in communication with said positioning member;

an actuating passage for communicating said spool valve with said solenoid-controlled valve; and

a plurality of fluid-conveying passages interconnecting the sump, the pump, the flow control valve, the solenoid-controlled valve, the spool-positioning cylinder, the housing and the motors.

4. in a numerically controlled rotary drive system wherein the system includes means for responding to electrical signals for triggering a change in machining modes, in combination, a hydraulic-actuated flow transfer assembly comprising:

a transfer valve housing having a spool bore therethrough intersected at axially spaced intervals therealong by fluid flow channels;

a valve spool reciprocable in said spool bore to control flow of fluid through selected channels, said spool and said bore forming a chamber at one end of said bore which communicates with one of said fluid flow channels in said housing and having a second chamber at the other end of said bore communicating with other of said fluid flow channels in said housing, and wherein said first chamber has a spool-stopping means and said second chamber has a spool-positioning means:

a fluid pressure source for supplying fluid under pressure to said transfer valve housing;

at least two reversible fluid-driven motors operatively connected for driving at least one output shaft, said motors being in communication with said transfer valve assembly through said fluid flow channels;

an electrically controlled actuating valve secured to said housing, said actuating valve being in communication with said first and second chambers through said fluid flow channels; and

an electrohydraulic reversing valve secured to said housing, said valve being in communication with said valve spool and said motors through said fluid flow channels adjacent said reversing valves ports;

so that said valve spool upon receiving a hydraulic signal generated by energizing said actuating valve moves said spool from a first position wherein said motors are connected in series with the reversing valve ports for lowtorque and high-speed operation to a second position wherein the spool connects said motors in parallel with the reversing valve ports for high-torque and low-speed operation, and which upon energizing said reversing valve reverses the flow through said motors thereby changing the direction of rotation of the output shaft.

5. The combination as recited in claim 4 wherein said spoolstopping means comprises:

a cylindrical member mounted to said housing and axially interposed within said first chamber.

6. The combination as recited in claim 4 wherein said spoolpositioning means comprises:

a hollow T-shaped as spool positioning member mounted to said housing and axially disposed within said second chamber, said member having a channel therein for communicating with said fluid flow channels in said housing.

7. The combination recited recited in claim 4 wherein the valve spool has a bore therein extending along the spools axis, said bore providing the means for slidably mounting the spool to said spool-positioning member, said bore also being under constant fluid pressure from said fluid pressure source by fluid communicated through said fluid flow channels in said housing and said channel within said spool-positioning member.

8. The combination as recited in claim 4 wherein the valve spool has three lands formed thereon, two end lands and one center land, said lands axially separated by two encircling spool grooves, and wherein the spool bore is encircled by four peripheral grooves, one of said grooves subject to being completely traversed by said center land when said spool moves from said first position to said second position and when moved from said second position to said first position.

9. The combination as recited in claim 8 provided further that the axial length of said center land is less than the axial length of said peripheral groove in the spool bore traversed by said center land when switching positions, so that the flow from one motor to the other motor will never be completely blocked off when switching from parallel operation to series operation and vice versa.

Patent No. ,635,022 Dated January l8, 1972 Inventor) Richard J. Lewis It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

IN THE SUMMARY Column 2, Line 26: "of" should read --or--- Column 2, Line 60: "force" should read ---forced--- IN THE DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Column 4, Line 60: "Fluid vexits motor M to the valve bore 2l should read --Fluid exits motor M through port 27 and re-enters valve bore 21 through port 29 by means of a channel 28 which connects motor M to the valve bore IN THE CLAIMS Claim l Column 7, Line 5: "low" should read --high--- Claim 6: Column 8, Line is} "as" should read --cylindrical--- Claim 7: Column 8, Line45: "recited" should read ---as-- Signed and sealed this 18th day of July 1972.

(SEAL) EDWARD M.FLET0HER, JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents F ORM P04 050 (0-69) USCOMM-DC 60376-P69 u.s. GOVERNMENT wnmrms OFFICE: mu 0-366-334 

1. A controllable condition rotary drive system for driving an output shaft comprising in combination: first and second reversible hydraulic motors adapted to be drivably connected to a common output shaft: a low-pressure fluid source; a low-pressure fluid sump; passage means interconnecting said fluid source and sump to said first and second hydraulic motors; motors; an electrically controllable reversing valve operative with said passage means to reverse the fluid source and fluid sump connections selectively in response to a first electrical signal and thereby reverse the direction of rotation of said hydraulic motors; a hydraulic transfer valve operative with said passage means to switch interconnection between said hydraulic motors from parallel to series fluid connection; and an actuating valve responsive to a second electrical signal to actuate said transfer valve to selectively switch between series and parallel fluid connection during either forward or reverse motor drive conditions; so that said common output shaft may rotate in either of two directions when said motors are either in a parallel or in a series fluid connection.
 2. A dual mode reversible drive system comprising in combination a low-pressure fluid sump: a high-pressure fluid source; a flow control valve, said valve supplied fluid from said fluid source; a solenoid-controlled valve, said valve supplied fluid from said fluid source; switching means which recEives fluid from said flow control valve, said switching means being activated by hydraulic signals from said solenoid-controlled valve; a pair of motors, said motors having reversible inlet and discharge ports, said motors being in communication with said switching means through said ports such that said motors operate either in a parallel or in a series relationship; and said motors drivingly connected to a single shaft.
 3. The combination as recited in claim 2 wherein said switching means comprises: a housing, said housing having a longitudinal cylindrical bore therein, said bore having a plurality of peripheral grooves separated by flangelike lands; said housing having a plurality of vertical passages intersecting said grooves forming a plurality of ports therein, a plurality of said passages being in communication with the flow control valve, and a plurality of said passages being in communication with the motors'' inlet and discharging ports; a spool-positioning member; a spool valve disposed in said cylindrical bore, said valve being axially aligned and in communication with said positioning member; an actuating passage for communicating said spool valve with said solenoid-controlled valve; and a plurality of fluid-conveying passages interconnecting the sump, the pump, the flow control valve, the solenoid-controlled valve, the spool-positioning cylinder, the housing and the motors.
 4. In a numerically controlled rotary drive system wherein the system includes means for responding to electrical signals for triggering a change in machining modes, in combination, a hydraulic-actuated flow transfer assembly comprising: a transfer valve housing having a spool bore therethrough intersected at axially spaced intervals therealong by fluid flow channels; a valve spool reciprocable in said spool bore to control flow of fluid through selected channels, said spool and said bore forming a chamber at one end of said bore which communicates with one of said fluid flow channels in said housing and having a second chamber at the other end of said bore communicating with other of said fluid flow channels in said housing, and wherein said first chamber has a spool-stopping means and said second chamber has a spool-positioning means: a fluid pressure source for supplying fluid under pressure to said transfer valve housing; at least two reversible fluid-driven motors operatively connected for driving at least one output shaft, said motors being in communication with said transfer valve assembly through said fluid flow channels; an electrically controlled actuating valve secured to said housing, said actuating valve being in communication with said first and second chambers through said fluid flow channels; and an electrohydraulic reversing valve secured to said housing, said valve being in communication with said valve spool and said motors through said fluid flow channels adjacent said reversing valve''s ports; so that said valve spool upon receiving a hydraulic signal generated by energizing said actuating valve moves said spool from a first position wherein said motors are connected in series with the reversing valve ports for low-torque and high-speed operation to a second position wherein the spool connects said motors in parallel with the reversing valve ports for high-torque and low-speed operation, and which upon energizing said reversing valve reverses the flow through said motors thereby changing the direction of rotation of the output shaft.
 5. The combination as recited in claim 4 wherein said spool-stopping means comprises: a cylindrical member mounted to said housing and axially interposed within said first chamber.
 6. The combination as recited in claim 4 wherein said spool-positioning means comprises: a hollow T-shaped as spool positioning member mounted to said housing and axially disposed within said second chamber, said member having a channel therein for communicating with sAid fluid flow channels in said housing.
 7. The combination recited recited in claim 4 wherein the valve spool has a bore therein extending along the spool''s axis, said bore providing the means for slidably mounting the spool to said spool-positioning member, said bore also being under constant fluid pressure from said fluid pressure source by fluid communicated through said fluid flow channels in said housing and said channel within said spool-positioning member.
 8. The combination as recited in claim 4 wherein the valve spool has three lands formed thereon, two end lands and one center land, said lands axially separated by two encircling spool grooves, and wherein the spool bore is encircled by four peripheral grooves, one of said grooves subject to being completely traversed by said center land when said spool moves from said first position to said second position and when moved from said second position to said first position.
 9. The combination as recited in claim 8 provided further that the axial length of said center land is less than the axial length of said peripheral groove in the spool bore traversed by said center land when switching positions, so that the flow from one motor to the other motor will never be completely blocked off when switching from parallel operation to series operation and vice versa. 